Try this:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = '.net, .net; C .NET Cobol .NET C++ .NET .NETER Perl IT x.NET 
+.net';
 ;;
 for my $kw (qw(.NET C C++)) {
   my $count = () = $s =~ m{ (?<! \S) \Q$kw\E (?: (?! \S) | (?= [,;]))
+ }xmsig;
   print qq{'$kw' $count};
   }
"
'.NET' 6
'C' 1
'C++' 1
[download]

There might be something a bit more elegant than  (?: (?! \S) | (?= [,;])) for the end delimiter, but it was a quick fix.